Change network policy label for the update proposals/votes and hw deleg certs

The update proposals and votes, and the heavyweight delegation
certificates are currently labelled as MsgTransaction for the purpose of
the network routing policy.

This means we can currently submit such objects from any node and they
will be forwarded to the core nodes. They are of course validated at
every hop.

For the purpose of the byron/shelley transition it will be simpler if
these objects are only submitted directly to the federated core nodes
and not via the relays.

So this patch changes the polciy so that these objects are not forwarded
by the relays. It does this by changing their label so that the existing
network routing policy treats them differently. So rather than being
labelled as MsgTransaction they are labelled as MsgMPC. The existing
policy for the MPC label is that relays do not forward such messages.

Author: dcoutts

lib/src/Pos/Diffusion/Full/Delegation.hs

@@ -49,7 +49,7 @@ pskHeavyRelay
     :: Logic IO
     -> Relay
 pskHeavyRelay logic = Data $ DataParams
-    MsgTransaction
+    MsgMPC
     (\_ _ -> postPskHeavy logic)
     -- The message size limit for ProxySKHeavy: a ProxySecretKey with an
     -- EpochIndex.
@@ -60,4 +60,4 @@ sendPskHeavy
     -> EnqueueMsg
     -> ProxySKHeavy
     -> IO ()
-sendPskHeavy logTrace enqueue = dataFlow logTrace "pskHeavy" enqueue (MsgTransaction OQ.OriginSender)
+sendPskHeavy logTrace enqueue = dataFlow logTrace "pskHeavy" enqueue (MsgMPC OQ.OriginSender)

lib/src/Pos/Diffusion/Full/Update.hs

@@ -85,7 +85,7 @@ proposalRelay logic =
     InvReqData
         NoMempool $
         InvReqDataParams
-           { invReqMsgType = MsgTransaction
+           { invReqMsgType = MsgMPC
            , contentsToKey = KV.toKey kv
            , handleInv = \_ -> KV.handleInv kv
            , handleReq = \_ -> KV.handleReq kv
@@ -104,7 +104,7 @@ voteRelay logic =
     InvReqData
         NoMempool $
         InvReqDataParams
-           { invReqMsgType = MsgTransaction
+           { invReqMsgType = MsgMPC
            , contentsToKey = KV.toKey kv
            , handleInv = \_ -> KV.handleInv kv
            , handleReq = \_ -> KV.handleReq kv